I'm new to javascript. My code (in the head section) below is not working for some reason. I know the problem is in the line " if (lfckv == 'true') " . It says "NOT ticked" when I check or uncheck the checkbox.

You have 2 problems.
1) You are trying to compare a boolean to a string when you should be comparing a boolean to another boolean.

2) You're using the double equals operator (==), not the triple equals operator (===).
The triple equals operator is better in 99% of cases. It does not do type coercion (Google it); it checks if the values are identical.

Here are some examples to show why you shouldn't use == (aka, the eqeq operator).